From 8a0996dacd89169668227f8668d8b8ba61c2f3a3 Mon Sep 17 00:00:00 2001
From: Johan Gustafsson <johan.gustafsson@campanja.com>
Date: Tue, 15 Nov 2016 22:03:48 +0100
Subject: [PATCH] basic promote_rule

---
 src/array.jl           | 10 +++++++++-
 test/13_arraycommon.jl |  3 +++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/array.jl b/src/array.jl
index e3a32aea..7450822b 100644
--- a/src/array.jl
+++ b/src/array.jl
@@ -1,7 +1,7 @@
 ## Common code for CategoricalArray and NullableCategoricalArray
 
 import Base: convert, copy, copy!, getindex, setindex!, similar, size,
-             linearindexing, unique, vcat
+             linearindexing, unique, vcat, promote_rule
 
 # Used for keyword argument default value
 _isordered(x::AbstractCategoricalArray) = isordered(x)
@@ -339,6 +339,14 @@ end
     @inbounds A.refs[I...] = get!(A.pool, convert(T, v))
 end
 
+@inline function promote_rule{T,N,R,T2}(::Type{CatArray{T,N,R}}, ::Type{Array{T2}})
+    CatArray{promote_type(T, T2), N, R}
+end
+
+@inline function promote_rule{T,N,R,T2<:Nullable}(::Type{CatArray{T,N,R}}, ::Type{Array{T2}})
+    NullableCategoricalArray{promote_type(T, eltype(T2)), N, R}
+end
+
 function mergelevels(ordered, levels...)
     T = Base.promote_eltype(levels...)
     res = Array{T}(0)
diff --git a/test/13_arraycommon.jl b/test/13_arraycommon.jl
index 9fe0a67b..e65deda9 100644
--- a/test/13_arraycommon.jl
+++ b/test/13_arraycommon.jl
@@ -280,6 +280,9 @@ for (CA, A) in ((CategoricalArray, Array), (NullableCategoricalArray, NullableAr
     @test x == ux
     @test typeof(x) == CA{Int, 1, UInt8}
     @test typeof(ux) == CA{Int, 1, CategoricalArrays.DefaultRefType}
+
+    @test promote_type(typeof(CA([3,2,1])), typeof([1,2])) == CA{Int,1,DefaultRefType}
+    @test promote_type(typeof(CA([3,2,1])), typeof(NullableArray([1,3]))) == NullableCategoricalArray{Int,1,DefaultRefType}
 end
 
 end